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Very-low-fat diet fails to improve heart health, UB study shows
By LOIS BAKER
Contributing Editor
In findings counter to current beliefs, a new UB study shows that a diet very low in fat does not lower the risk factors for heart disease in healthy sedentary individuals and, in fact, may increase them.
The pilot study, involving 11 persons, found that consuming a diet restricted to 19-percent fat significantly lowered the amount of "good" cholesterol (HDL-C) and apolipoprotein A1 (ApoA1), the major transport protein for HDL particles, compared to diets based on 30-percent and 50-percent fat.
In addition, a 50-percent-fat diet did not affect total cholesterol or other factors associated with heart-disease risk when caloric intake and expenditure were kept equal.
Results of the study appeared recently in the Journal of the American College of Nutrition.
"We're aware that these findings go against most peoples' thinking," said David Pendergast, professor of physiology and biophysics in the School of Medicine and Biomedical Sciences and corresponding author on the study. "However, consumers have been falsely convinced by information that is not supported by scientific data.
"For decades, low-fat diets have been advocated for weight reduction and to lower the risk of coronary heart disease," said Pendergast, "but randomized controlled trials haven't confirmed that low-fat diets accomplish this or can be sustained for the long term. In fact, total fat intake when caloric intake is balanced to expenditure shows little correlation with CHD," he said. "It's consuming more calories than you expend that harms health."
Pendergast and colleagues set out to determine the nutrient status and certain cardiovascular risk factors of healthy sedentary men and women who consumed diets composed of 19-percent, 30-percent and 50-percent calories from fat. Prior to the dietary intervention, the 11 participants kept a seven-day food intake and activity record, and provided a list of food preferences. The food records showed that the participants' regular diets contained 30-35 percent fat, which then served as the control. Fasting blood samples were taken at baseline and after each dietary intervention.
Researchers calculated each individual's metabolic rate—the rate at which the body burns calories—and used this measure to prescribe a diet that matched caloric intake with caloric expenditure, while including servings from all the food groups. The two intervention diets—either 19-percent or 50-percent calories from fat—had the same proportion of saturated, monosaturated and polyunsaturated fatty acids. Protein intake was set at 20 percent of total calories for all diets, but the actual percent protein intake turned out to be lower on the 19- and 30-percent-fat diet than on 50-percent-fat diet.
The intervention diets were assigned randomly and the analyses were blinded to the assignments. Subjects remained on each intervention diet for three weeks and kept diaries of daily activities and food intake after each meal, which they turned in weekly. Dieticians followed up with the subjects weekly to make sure they were complying with their diets.
Fasting blood samples were taken at the end of each three-week period. Participants returned to their regular diets for a week, termed a wash-out period, before beginning the next intervention.
Blood-sample analysis showed that HDL-C, the good cholesterol, was highest on the 50-percent-fat diet and that Apo A1, an important transporter of HDL-C, increased on the two higher-fat diets compared to the 19-percent-fat diet. Pendergast said this result, which seems counterintuitive, is explained by the fact that dietary fat stimulates production of an enzyme stored in muscle that increases ApoA1 activity, which in turn brings more HDL-C into the muscles and other tissues. The lower HDL-C and ApoA1 on the low-fat diet likely is due to decreased ApoA1 transport rates, he said. In addition, essential fatty acids, Vitamin E—a powerful antioxidant—and zinc—an essential mineral—increased as dietary fat increased.
Meanwhile, increasing the fat content of the diet from 19-to-30-to-50 percent over the short term caused no increase in body weight, body fat, blood pressure, resting heart rate, blood glucose or lipoproteins, all would-be indicators of heart-disease risk, results showed.
"These findings support the notion that if total caloric intake is balanced to expenditure, body weight will remain constant and increasing the amount of fat in the diet in and of itself will not have a negative effect on blood cholesterol," said Pendergast. "In addition, very-low-fat, high-carbohydrate diets may not reduce heart-disease risk. We have shown that if you maintain a very-low-fat diet, you miss some essential macro and micro nutrients."
"Sedentary Americans should eat a palatable blend of healthy fats and good carbohydrates—those with low glycemic index and high in fiber—while spending more calories than they consume by increasing their activity."
Additional researchers on the study were graduate students Kluwara Meksawan and Melanie Mason, faculty members Peter J. Horvath and Atif Awad, all from the Department of Exercise and Nutrition Sciences in the School of Public Health and Health Professions, and John J. Leddy, assistant professor of orthopaedics in the medical school.